Hat-making or millinery is the design, manufacture and sale of hats and other headwear. A person engaged in this trade is called a milliner or hatter.

Historically, milliners (typically women shopkeepers) produced or imported an inventory of garments for men, women, and children and sold these garments in a millinery shop. Many milliners worked both as milliners and as fashion designers, such as Rose Bertin (1747-1813), Jeanne Lanvin (1867-1946), and Coco Chanel (1883-1971).

The millinery industry benefited from industrialization during the nineteenth century. In 1889 in London and Paris, over 8,000 women were employed in millinery, and in 1900 in New York, some 83,000 people, mostly women, were employed in millinery. Though the improvements in technology provided benefits to milliners and the whole industry, essential skills, craftsmanship, and creativity are still required. Since the mass-manufacturing of hats began, the term "milliner" is usually used to describe a person who applies traditional hand-craftsmanship to design, make, sell or trim hats primarily for a mostly female clientele.

The term "milliner" or "Milener" originally meant someone from Milan, in northern Italy, in the early 16th century. It referred to Milanese merchants who sold fancy bonnets, gloves, jewellery and cutlery. In the 16th to 18th centuries, the meaning of "milliner" gradually changed in meaning from "a foreign merchant" to "a dealer in small articles relating to dress". Although the term originally applied to men, from 1713 "milliner" gradually came to mean a woman who makes and sells bonnets and other headgear for women.